The present invention relates to reactors in which entrainment-controlled mixing of products and reactants is important, and to the feed pipes and nozzles used in such reactors for feeding reactants thereto. More particularly, but without limitation, the present invention relates to reactors and feed pipes and nozzles for the production of chloromethanes and other useful chlorinated derivatives by thermally-initiated adiabatic, vapor-phase chlorination.
Typically chloromethanes and these other chlorinated derivatives are produced in a gas phase chlorination reactor apparatus which consists of a pipe feeding into a larger diameter vessel. Chlorine and organic reactants such as methyl chloride and methylene chloride are premixed in the feed pipe, and fed into the larger vessel at high velocities but at temperatures which are insufficient to initiate the chlorination reaction. Hot, already reacted product gases are entrained into the high velocity feed stream as the stream expands into the reactor and moves along the reactor's length, however, and provide the necessary heating to initiate and propagate the chlorination reaction. As reactants continue to be fed into the reactor, hot product gases are continuously recirculated back toward the inlet of the reactor in a "self-stirring" mechanism.
A primary goal in the design of any high temperature, vapor-phase chlorination reactor apparatus, or in the retrofitting of an existing apparatus, thus is to ensure that adequate self-stirring of the products and reactants occurs in the reactor. In general, though, the amount of entrainment and recirculation that can be achieved in a typical sudden expansion-type reactor apparatus, as by using a smaller nozzle to create higher feed velocities, is limited.
Achieving a greater degree of recirculation and self-stirring would have a couple of very significant benefits. Unreacted chlorine tends to have a significant corrosive effect, and greater recirculation and self-stirring improve the chlorine conversion over a reactor of a given length so that less corrosion of downstream equipment occurs. In addition, improved self-stirring increases the critical flowrate at which the reaction is quenched or "blown out". At high reactant flow rates, the rate of heat removal by convection may exceed the rate of heat generation by reaction of the incoming reactants. Improved self-stirring feeds back more of the heat of reaction to the incoming reactants.
The chlorination reactor art reveals several attempts at achieving greater mixing of products and reactants. For example, in U.S. Pat. No. 3,054,831 to Samples et al. a halogen gas such as chlorine is fed into a reactor through a jet nozzle, which jet nozzle in turn feeds into a venturi tube. The venturi tube is provided with ports or is open at its upper end so that hydrocarbon reactant and hot product gases from the reactor can be drawn into and through the venturi by the passage therethrough of the high velocity chlorine gas from the jet nozzle. The hydrocarbon reactant is fed tangentially into the reactor through an inlet pipe at about the level of the discharge end of the venturi.
In U.S. Pat. No. 3,522,017 to Barfield, Jr., a similar device is disclosed in which the several gaseous reactants are premixed and discharged through an actuating nozzle threaded into a bottom wall of the reactor. The actuating nozzle tapers down to a small cross-section and discharges the premixed reactant gases at high velocity into a larger diameter, slightly inwardly tapering tube, the tube being preceded however by inlet slots or ports so that reactant and product gases already in the vessel can be entrained in the high velocity gas stream from the actuating nozzle. The tube delivers the gases into a diffuser/expander which divergently sprays the gases into the reactor volume.
And in U.S. Pat. No. 4,590,044 to Mos et al., a first reactant in traveling a zigzag path through successive reactor stages is contacted in some stages by a cross-currently injected second reactant at a high temperature and a high velocity, and in other stages by opposed high velocity, cross-currently injected high and low temperature streams of the second reactant. Effective mixing of the first and second reactants and of formed products is said accomplished by the differences in velocity of the first and second reactant streams into the reaction space.
The primary drawbacks of these other devices are their complexity and expense of manufacture compared to a sudden expansion-type reactor, and the related difficulty or impossibility of practically and economically applying the features of these devices to retrofitting and upgrading an existing chlorination reactor apparatus.